it works by using known radio sources (ie tv transmitters) which has the advantage of being powerful , continuous and reasonably unique signal pattern (for timing)
radio sniffing is where you listen for the aircraft directly, and there are a number of offerings on that front too. Phased array antenna with SDR front ends, are smashing bits of kit.
now frequency hopping spread spectrum means you need more DSP to find the signal, but its still there. In fact it provides nice timing signals because they hop frequency so much. There is more, but thats for another time
In theory the frequency hopping can be random, but that requires a shared random source, which is hard to sync.
That's not really radar though. Radar systems have a dedicated transmitter that broadcasts. Phased array radars have transmitters as well. What you're describing is more akin to ESM. Conflating the two definitions diminishes both. It's like when submarine movies depict sonar using a hydrophone without a transmitter; that's passive compared to real sonar that creates a ping.
Passive and active are both valuable in their own regimes, but they're not the same.
it works by using known radio sources (ie tv transmitters) which has the advantage of being powerful , continuous and reasonably unique signal pattern (for timing)
radio sniffing is where you listen for the aircraft directly, and there are a number of offerings on that front too. Phased array antenna with SDR front ends, are smashing bits of kit.
now frequency hopping spread spectrum means you need more DSP to find the signal, but its still there. In fact it provides nice timing signals because they hop frequency so much. There is more, but thats for another time
In theory the frequency hopping can be random, but that requires a shared random source, which is hard to sync.